French Patent FR 2 793 085 describes an alternator for a motor vehicle, comprising a stator and a rotor. The rotor assembly comprises a winding and two rotors each equipped with a plurality of claws. The rotors define between themselves, on a level with the claws, inter-rotor spaces each able to accommodate a permanent magnet structure, in particular made of rare earth. The direction of magnetization of these magnet structures must be alternating from one inter-rotor space to the next. For this purpose, these magnet structures are arranged in two distinct groups, according to their direction of magnetization. However these two groups cannot be distinguished visually. Thus when the magnet structures are assembled in the inter-rotor spaces of the rotor, special care must be taken to select the magnet structures with the correct direction of orientation.
U.S. Pat. No. 7,095,154 describes an alternator rotor assembly comprising permanent magnets held in inter-rotor spaces by means of support elements. Each magnet is positioned in a non-centric way in the corresponding inter-rotor space.